Gains: A skill or possession is obtained without any loss, except perhaps time and effort. A life of gains is one of gradually increasing skill, wealth, and status.

Trade-ups: Something is given up in order to obtain something better. A transformation takes place. A life of trade-ups has very distinct stages.

The difference is that a gain can be given up, but a trade-up might not allow a trade-down. A forced gain is only somewhat creepy but a forced trade-up is very creepy. Even a voluntary trade-up is borderline creepy, it's non-reversible and the choice might not be fully informed. The social norm we are heading toward is that consent can be withdrawn at any time, and any trade-up violates that.

Applications:

In the stories we tell, the class of life events characters experience is extraordinarily heavily stereotyped by gender.

This explains the creepiness of certain authors: Walt Disney, Steven Moffat, Anne McCaffrey, Iain Banks. A form of pornography in which the imagined universe satisfies the desires of the author, in which violence becomes inescapable physics.

It explains the odd quality of certain other authors: Cory Doctorow, Peter Watts, William Gibson, Kurt Vonnegut, Greg Egan. The physics of the imagined universe does not titillate and reassure, it horrifies, it acknowledges a truth about the world or about the author, and the characters fight against it.

See also: James Watson. While describing Rosalind Franklin, possibly the discoverer of the structure of DNA, certainly the person who's crystallography skill made it possible: "In this new edition, I notice that Ray [Gosling - her student] has rather a good line in response to my comments about her appearance. He notes that I never saw her dressed up to go out in the evening, and that she had an elegance that I probably never saw." Watson, and I say this with perfect sincerity, go eat your own shit. What utter inability to perceive the greatness of one of our greatest scientists, just because it doesn't fit your gendered schema.